1. Field of the Invention
The present invention relates to technologies for displaying stereoscopic video images, and in particular to a technology to stereoscopically superimpose an on-screen display (OSD) on stereoscopic video images.
2. Description of the Related Art
Technologies for displaying stereoscopic video images are promising as a display technology for the next generation, and have been rapidly developed in recent years. Basically, the technologies use the following fact: “Persons perceive the three-dimensional shapes and depths of objects from binocular parallax” (See Non Patent Document 1 for example). More specifically: first two video frames in a single scene are shot; the same object has slightly different locations in the horizontal direction in the two video frames; and then one of the two video frames is projected to the left eye of a viewer, and almost simultaneously, the other video frame is projected to the right eye of the viewer. As a result, the viewer perceives the three-dimensional shape and depth of the object from the slight displacement of the object between the video frames projected to the respective eyes.
As seen from the example explained above, the technologies for displaying stereoscopic video images generally require two video frames to display a single scene, one for the left eye and the other for the right eye. This means that the data size of stereoscopic video images for a given length of display time is generally larger than that of conventional two-dimensional video images. Thus, a large-capacity optical disc such as a Blu-ray disc (BD) and a disc drive therefor are necessary for playback of stereoscopic video images.
Conventional two-dimensional video display devices and optical disc drives generally have an OSD function. The “OSD function” means a function to display graphics images on the screen of a display device, the graphics images representing, for example, a settings screen for screen brightness, the volume of sound, etc.; information showing operational states such as “Start playing” and “Pause”; or a selection screen for a title and a chapter to be played back. Such graphics images are called “OSDs”. In addition, some playback devices for playing back high-quality video images from a read-only BD (BD-ROM disc) have a function to render graphics images on the high-quality video images according to an application program recorded on the BD (See Patent Document 1 for example). Providers of video contents enable the playback devices to realize sophisticated graphical user interfaces (GUIs) by causing the playback devices to render pop-up displays, animations, and the like. Thus, stereoscopic video display devices and playback devices are also demanded to have similar OSD and graphics rendering functions.
An example of a stereoscopic video playback device having such functions is known, which can render a stereoscopic image of a mouse cursor on other stereoscopic images (See Patent Document 2 for example). This playback device generates two types of graphics images which represent the mouse cursor on a screen at slightly different locations in the horizontal direction, and superimposes one of the graphics images on left-view video images, and the other on right-view video images. When the mouse cursor is displayed in the same view direction as a different object in the stereoscopic video images at the same time, the playback device changes the displacement of the mouse cursor between the left-view and right-view video images from the displacement of the object therebetween by a predetermined amount. With this operation, the playback device allows the viewer to see the mouse cursor in front of the object.